Hypoxia/anoxia is a well-characterized component of the microenvironment of most solid tumor. Considerable experimental and clinical evidence supports the notion that hypoxia fundamentally alters the physiology of the tumor towards a more aggressive phenotype. The Unfolded Protein Response (UPR) is a cellular stress adaptation pathway which promotes cell survival in the presence of Endoplasmic Reticulum (ER) stress, including physiological stress in the tumor microenvironment. The PERK/eIF2a/ATF4 pathway reduces the global rates of protein translation thereby alleviating metabolic stress under hypoxia while at the same time induces the translational upregulation of important chaperones and pro-survival genes. Another UPR component is the activation of the endonuclease/kinase IRE1 and its immediate effector XBP1, which activate a transcriptional program aimed at increasing the folding capacity of the ER. Recent in vitro and in vivo studies from the labs of the two co-PIs, have shown that transformed cells with ablated UPR responses exhibit reduced tolerance to hypoxia in vitro and form tumors that are slower growing compared to tumors grown from cells with an intact UPR, indicating that UPR activation contributes to tumorigenesis. In preliminary studies, we have developed cell-based and animal-based assays for UPR activation and its inhibition by small molecules. The overall goal of this proposal is to validate UPR activation as an important anti- tumor target and to use novel in vitro and in vivo assays to identify potent inhibitors of this response as novel chemotherapeutic agents. In Aim 1, we will employ in vitro reporter assays of PERK activity to identify specific inhibitors of the PERK/eIF21/ATF4 pathway and test the effect of combined administration of these inhibitors with inhibitors of the IRE-1 pathway (Irestatins) on tumor cell survival under normoxia and hypoxia. In Aim 2, we will investigate the potential synergy between inhibitors of the PERK and IRE1 pathways with the proteasome inhibitor Bortezomib in killing hypoxic tumor cells in vitro and in vivo. Studies under Aim 3, will evaluate the use of Zebrafish as a model system to analyze the ability of inhibitors of the PERK and IRE1 pathways to inhibit xenotransplanted human tumors and to inhibit angiogenesis without causing significant developmental abnormalities. Finally, in Aim 4 we will test the efficacy and potential toxicity of identified compounds in mouse tumor models. We expect that these efforts will culminate in the development of specific and potent inhibitors of the UPR which alone, or in combination with existing antitumor agents and modalities will be effective in reducing tumor burden in preclinical and clinical malignancies. PUBLIC HEALTH RELEVANCE: A hallmark of solid tumors is the requirement to adapt to, and eventually overcome the stressful environment of low oxygen, growth factors, glucose and pH in the growing tumor mass. The requirement for neoangiogenesis to support tumor growth is now well established and is the basis for several promising anti-tumor modalities. Based on published data from our labs and others, we propose that the Unfolded Protein Response also plays a crucial role in adaptation to hypoxic stress, and like angiogenesis, represents an encompassing and stable aspect of tumor development and thus provides a unique opportunity for therapeutic exploitation. This proposal aims to identify agents that target key components of this adaptive response has the potential to offer additional and novel approaches to target the very stresses that hinder existing anti-tumor treatments and thereby improve antitumor treatment efficacy.